For many purposes it is required to provide a temperature-controlled, high-vacuum environment. Heretofore it has typically been the practice to achieve a high vacuum by interconnecting a diffusion pump to a port of a chamber in which the vacuum is to be established. Temperature control is effected by including a heater and thermal insulation system to mantain the vacuum chamber at a desired operational temperature. In these prior art systems, a separate heating system is employed to heat the working fluid in the diffusion pump to its operating temperature. If, as is typically required, an extremely low contamination atmosphere is to be maintained in the chamber, the diffusion pump must be separated from the vacuum chamber by a cooled trap or vapor baffle arrangement. Thus, conventional systems having duplicate high temperature zones separated by a relatively low temperature zone and composed of separate elements tend to be bulky and expensive to fabricate and operate.
In accordance with the illustrated preferred embodiments, the present invention provides a diffusion pump, including an internal high-vacuum chamber which is surrounded by the working vapor sections of the pump. An instrument requiring a high-vacuum environment may be inserted into the internal chamber. Gas molecules to be evacuated from within the vacuum chamber drift into the vapor pumping region of the pump where they are swept out of the pump by the high velocity working vapor molecules.
In preferred embodiments of the invention, both the working fluid of the diffusion pump and the vacuum chamber itself may be heated by a single heating unit. The heated regions are generally surrounded by a relatively low temperature zone required for working vapor condensation, thus eliminating the need for thermal insulation. To prevent potentially contaminating working vapors from entering the high vacuum chamber, a simple cold cap and cooled baffle may be included.
In accordance with further embodiments, a differential pump is provided in which a common boiler provides working vapor for a pair of pumping units configured so that one of the pair evacuates a first chamber, while the other evacuates a second chamber. These two chambers may be connected by an aperture. Thus, if the device is utilized in conjunction with an analytical instrument such as a gas chromatograph-mass spectrometer (GC/MS) instrument, the first chamber may house the MS ion source and be connected directly to the effluent of the GC while the second chamber houses the MS analyzer. This permits the MS to accept a large fraction of the effluent, or all of the effluent, as desired, from the GC; the first pump need only establish a reasonably low pressure required for the ion source, and can therefore handle a large incoming flux, while the second pump can establish a much lower pressure required by the mass analyzer, since only a small flux enters the second chamber through the aperture from the first chamber. Differential pumping is thereby simply obtained.